Schizophrenia is a complex syndrome that may preferentially affect the temporal lobes. One possible structural correlate is a shift in the amount and patterns of cortical folding (gyrification). A morphometric measure of relative gyral development will test several hypotheses in the temporal lobes. the measure is the gyrification index which is a ration of the total cortical contour divided by the cortical contour which is superficially exposed. As the measure is relative, it does not change when the lobes are processed differently and so MR images and histological sections can be compared directly. A preliminary study on the gyrification index in monozygotic twins discordant for schizophrenia shows a possible difference in the right temporal lobe at the level of the rostral hippocampus. The hypotheses to be tested are as follows. 1_0 Schizophrenic and normal temporal lobes differ in their patterns of gyrification and this difference will be found on the medial temporal lobe and not on the lateral. 2) The normal variation in patterns of temporal lobe gyrification does not overlap that of schizophrenia. 3) No consistent lateralization in the gyrification index are normally found between the two temporal lobes, but they are present in schizophrenia. 4) During ontogeny, the development of temporal lobe gyrification does not increase in a smooth rostrocaudal wave, but shows some topographic independence. 5) Temporal lobes with atrophic changes will show a different pattern of gyrification indices than those observed in normal and schizophrenic brains.